Support viewport-relative widget sizing

src/event_loop/app_data.rs

@@ -411,6 +411,7 @@ impl<A: App> AppData<A>
 		// configure.new_size is surface-local (logical), so multiply by the
 		// current buffer scale before handing the dimensions to the app.
 		let sf = self.main.scale_factor.max( 1 ) as u32;
+		self.app.on_scale_changed( sf );
 		self.app.on_resize( w * sf, h * sf );
 		// `on_resize` may flip app-state that the view depends on (apps that
 		// branch on the new dimensions, layout caches keyed by size, …), so